Apparatus for determining the moisture content of insulated boots and similar articles



Sept. 26, 1961 I Djw. BATTEAU 3,002,150

APPARATUS FOR DETERMINING THE MOISTURE CONTENT OF INSULATED BOOTS AND SIMILAR ARTICLES Filed Aug. 28, 1959 3 Sheets-Sheet 1 F I WHEATSTONE I I CYCLE BRI GE AMPLIFIER RECTIFIER METER OSCILLATOR D I l a :o 12 l 2 6 INDICATING LIGHT l4 F|G.I

OSCILLATOR (d) INVENTOR.

DWIGHT W. BATTEAU ATTORN EYS Sept. 26, 1961 D. w. BATTEAU 3,002,150

APPARATUS FOR DETERMINING THE MOISTURE CONTENT OF INSULATED BOOTS AND SIMILAR ARTICLES 3 Sheets-Sheet 2 Filed Aug. 28, 1959 FIG. 3

IN V EN TOR.

DWIGHT W. BATTEAU ATTORNEYS 3 Sheets-Sheet 3 R N E r w W 4 'lllr/lllllllll N A 3 4 I B n 1 I 8 7 w ld'll'l'llll'fllllll I W 4 q T 7 2 H 5 m a 4 M7 6 AT ORNEYS Sept. 26, 1961 D. w. BATTEAU APPARATUS FOR DETERMINING THE MOISTURE CONTENT INSULATED BOOTS AND SIMILAR ARTICLES Filed Aug. 28, 1959 United States Patent.

3,002,150 APPARATUS FOR DETERMINING. THE MOISTURE CONTENT OF INSULATED BOOTS AND SIMI- LAR ARTICLES Dwight W. Batteau, Cambridge, Mass., assignor to Flow Corporation, Arlington, Mass., a corporation of Massachusetts Filed Aug. 28, 1959, Ser. No. 836,723 2 Claims. (Cl. 324-61) This invention relates toapparatus for measuring the moisture content of articles of irregular shape and more particularly to novel apparatus for supporting the articles to be tested.

In its illustrated form, the present invention is designed Specificallyto test winter footwear such as infantrymens combat boots, but it may be adapted to determine the moisture content of other articles as well.

It has been determined that the thermal insulating property of winter footwear of the type having a fleece lining sandwiched and hermetically sealed between inner and outer layers of rubber or other flexible impervious material is materially affected by the moisture content of the lining. So long as the moisture content of the lining is below a certain level, the boot or shoe will provide satisfactory insulation against frostbite at relatively low temperatures. However, when the moisture content exceeds that level, there is a marked decrease in insulating power and frostbite will occur much more readily.

This phenomenon being known, it is very important that each insulated boot be measured for moisture content and that onlythose boots having less than the maximum permissible moisture content be released for use.

Heretofore, however, there has been lacking a device or method capable of reliably and rapidly determining the moisture content of an insulated boot without penetration or at least partial destruction of the boot under test. Prior non-destructive methods and devices have failed to give consistent results on repeated tests of the same boot. Accordingly, the object of this invention is to provide a novel method and apparatus for rapidly determining the moisture content of insulated winter footwear and similar articles without injury thereto.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the invention becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a block diagram of a moisture-measuring system constructed according to the present invention;

FIG. 2 is .a circuit diagram of the Wheatstone bridge forming part of the systemof FIG. 1;

FIG. 3 is a perspective view of a preferred embodiment of the present invention;

FIG. 4 relates to the same apparatus as FIG. 3 and is a vertical section taken along line 44 of FIG. 5; and

FIG. 5 is a vertical section taken along line 5-5 of FIG. 4. I

The present invention provides a measure of the moisture content in a bootwithout penetratingor destroying it, by measuring the total change in the. dielectric factor of a capacitor containing the boot. The dielectric constant of water at 20 and low frequencies is 80, compared to 1.0 for a vacuum, 1.0003 for air, and approximately 2.6 for rubber. Thus, a small quantity of water introduced into a capacitor can cause a large change in its capacitance. Since the change in total capacitance caused by water is proportional to the quantity of water, measurement of capacitance change resulting from the water alone can be utilized to provide a measure of water content.

Application of this principle to an insulated rubber in boots of the same size.

' Patented Sept. 26, 1961 boot can be effected by placing the boot between the plates of a capacitor. When this is done, the dielectric factor of the capacitor is increased by an amount depending not only on the moisture content but also on' the amounts of the other materials, i.e., the rubber and wool, their dielectric constant, and their locations. For a given style of boot, the total amount of rubber and wool varies according to boot size and will even vary However, since the dielectric constants of dry rubber and dry wool are relatively small, the changes in total capacitance resulting from variations in sizes of the boots are relatively small compared to the changes produced by even small changes in water content. Thus, the effect of water is easily separated from the effect of the dry rubber and wool. The change in capaci tance due to relative locations of materials is standardized by the boot shape which remains substantially constant for a given style of boot. However, since a boot is of irregular shape, its orientation relative to the plates of the capacitor will also effect the total capacitance, and significant changes in total capacitance will result by merely changing the position of the boot. For this reason, it has been found necessary to provide a capacitor whose geometry is particularly adapted to minimize the elfect of orientation of the boot.

FIG. 1 is a block diagram of a complete system embodying the present invention. The system may be broken down as follows: an oscillator 2, a Wheatstone bridge 4, and a detector 6 comprising an amplifier 8,

a rectifier 10 and'an output meter 12; and as an optional feature, a light indicator 14.

. In this case, the oscillator is a Colpitts oscillator producing a 1 kc. output. As shown in FIG. 2, the Wheatstone bridge 4 comprises four series-connected resistors R1, R2, R3, and R4, a variable capacitor C2 connected acrossresistor R2, and a specially designed boot-holding capacitor C4 connected across resistor R4. Capacitor C2is of the type having a calibrated dial. The boot holding capacitor is illustrated in FIGURES 3-5 and is described in detail hereafter.

The output of oscillator 2 is applied to the bridge at points a and c. Detector 6 is across points b and d.

When the voltage drop from point (a) to point (b) is the same as from point (a) to point (d), no. current will flow through the amplifier, and the meter will read zero. The following equations represent the two conditions which must be obtained if no current is to lie in the detector:

. "Bld R and R, are fixed, thereby enabling the following mathematical statements:

c,=k.c, and R,=='K.R,

where k and K are simply constants of proportionality.

and R102 R3 4 Since the problem is to ascertain boot-holding capacitor C4, itis sufficient to adjust R2 and C2 until the bridge is balanced and then observe the value of C2 as indicated on its calibrated dial. j .J Since the value of C2 is a function of the water con.- tent of the boot under test, the dial of C2 may be. cali brated directly in terms of water content or the amount of water in the boot under test may be determined by a calibrationcurve which compares variations in value of C2 with water content. Separate calibration curves may be set up for different types of boots.

The full wave rectifier circuit 10 is connected across the amplifier load circuit and provides direct current for the meter 12. When the meter reads zero, the bridge is balanced and the value of C2 indicates the water content.

For production testing, an indicator light 14 can be coupled to the bridge so as to go on at a selected p: sition of C2. This selected position may be the one obtained when balancing the bridge for a standard boot, i.e., a boot whose water content is known and is at or just below the maximum or threshold value. Thus, in testing for a boot, the operator need not read the dial but need only observe whether alight is turned on when the meter needle reads zero.

It has been determined that in order for the system to be accurate with minimal operator skill and with no significant deviation in result due to orientation of the boot, the capacitor C4- should be'spherical, made up of one bail within another, with the two 'ballsin substan.-

tially symmetrical-spaced relationship. This construction has the advantage that in use the inner ball inside the boot, providing support and facilitating location of each boot in a standard position. The effect of orientation of the boot is minimized because a given amount of material will produce the same effect so long as it is the same distance from the surfaces, regardless of angular location.

FIGS. 3-5 illustrate the spherical capacitor of the present invention. FIGS. 3.1-5 show, a housingltl made upof a bottom wall 24, a top wall '26, and side walls '23. The casing is supported by suitable 'legs30 attached to bottom wall 24.

Top wall 26 is formed witha circular opening in which is secured a large bottom hemisphere 32.. The

marginal portion or mouth of hemisphere 32 projects above top wall 26 and is flared as at 34. The hemisphere may be supported solelyby its marginal portion acting on .top wall 26; or, ifdesired, screws ;37 maybe driven through the hemisphere laterally {into top wall 26.

Hemisphere 32 has an opening at its bottom in which is secured a coaxial connector 36. Coaxial connector 36. supports a long brass rod 68 whichextends radially of the hemisphere. Surrounding :brassrod 33 and at- .tached to hemisphere 32 by. screwswgttlis ahollow post 52 formed of plastic. Post .42 has a plurality of thin -sec'to13shapecl webs .44. One of the webs 44 wider than the rest. The top endof ,post 5&2 has ,a concave depression as. Seated on the concave suriace ts is a smaller hemisphere whose mouth has a ;fiared rim 5 2. Hemisphere St is secured to post142 by a short post 56. The bottom .end of post 56 extends through a holein hemisphere 50 and is provided with external threads 58 which are screwed into a tapped hole provided in the top end of post 42. Securedto the top end of post 56 by means of ascrew .60 is a small top hemisphere 62. The edge of, hemisphere 62'fits-within rim 52 of bottom hemisphere 50. Post 56 has a central bore 64 into which extends the uppe r end of rod 38. Post 56 also has a'lateral opening in which is mounted a set screw 66. Set screw 66 engages rod 38 and operates ;to electrically couple. post 5 6 andhemisphere '50 and 62 to the brass rod. The br ass rod38 and bottom hemisphere 32 are coupled by coaxial connector 36, a cable 68, and another coaxial connector 70 to appropriate points in an instrument housed ,in a .case 14 and em- "bo'dving the system of FIGS. -1 and :2.

,Attached to the top wall 26 of the case -20 are two .bearingblocks and 82' which-rotatably support ashaft 84. Shaft 84 is secured to a bracket. which is :formed integral with a top hemisphere .88. Attached to shaft 5 84 atthe-opposite ends thereof :are two arms and 9.2,

i which extend into case 29 through slots as. The upper ends of these arms are provided with suitable grips 96. Arms 90 and 92 are bent at a point located below shaft 84 and their bottom ends are connected to each other by a cross bar 9 8. The latter carries a counter weight member res. Arms 90 and 92 are bent at an angle such that when the hemisphere 83 is pivoted to open position as shown ineach of the figures, the counter weight will be at its lowest position and will act to-hold the h ll SP Q' PP P: I i v i The four hemispheres and the connecting post 56 are all constructed of aluminum. The puter hemispheres have an anodized finish: The center" post '42 may be formed of any suitable plastic, preferably polystyrene or methylmethacrylate polymer.

As shown in dotted outline in :FIG. 4, a boot to be tested is placed over the inner sphere and post 42 and is positioned with the toe of the boot located, directly above web 44a. Web 441 serves as apositioning g ide so that each boot will automatically assume the same angular position and also to support and hold open the expansion pleat on the front of the upper part of each boot.

With the boot in place, thetop hemisphere is closed by manipulation of arms )0 and 92 and the instrument operated to determine its moisture content.

Obviously, many modifications and variations of the invention'are possible in the light of the above teachings. It -is to be understood, therefore, that the invention ,is not limited in its application to the details of construction and arrangement of .parts specifically described or illustrated, and that within the scope of the appended claims, it may be practiced otherwise than as specifically described or illustrated.

I claim:

1. Apparatus for measuring the relative water content of articles by im easuring their relative capacitance, said apparatus having :in combination; a basej a capacitor mounted on said-base having a first .and second electrode in electrically insulated relation, said first electrode being substantially spherical in configuration, said second electrode being hollow and at least in part spherical and arranged around and concentrically with" said first electrode; said electrodes being spaced apart to receive said articles, whereby the capacitance of said articles placed between said electrodes is added to the fixed capacitance between said electrodes and distortions in the combined capacitance of said electrodes and said articles due to variations in'the position of said articles are'mmimized; means including a balanced bridge circuit for measuring an unknown capacitance; and said capacitor connected to said measuring means in the position of the said unknown capacitance.

2. The apparatus defined in claim 1, further characterized by said first electrode constructed and arranged with respect to asaid article having a relatively hollow configuration to fit therein and support the same with said articlesubstantially surrounding said first electrode, whereby the saidarticle influences the dielectric field of said capacitor substantially .toits extent. 

